Rotary presses serve, as is generally known, for producing tablet shaped pellets, in particular, for the pharmaceutical industry. Rotary presses have largely the same construction. A rotationally driven rotor contains upper and lower punches and dies, into which powdered press material is filled continuously with the use of a filling device, and the powdered material is compressed using the press punches. The press punches are actuated using pressure rollers. Outside of the press stations, the press punches are controlled by control cams. After pressing, the pellets are ejected using the lower punches, and removed from a deflector.
In the pharmaceutical sector, in particular, the pellets must meet a series of quality criteria, for example, weight, strength, break resistance, height, active substance content, active substance release, dispersal, friability, porosity, surface, moisture content, etc. It is known to perform quality surveillance through sampling during production. If the tested pellets do not correspond to the desired conditions, appropriate setting parameters in the press are changed. Setting parameters are, for example, the rotational speed of the rotor, the rotational speed of the filling device, the powder dosing into the dies, the pressing force over the pressure rollers, etc.
Online process control is also known. A test device is positioned directly alongside the tablet press. Samples are automatically removed from the tablet flow and guided to the testing device. There, the pellets are isolated and measured. A change of at least one setting parameter of the lower press occurs via a computer interface from the testing device to the machine control. It is generally known to assign to such rotary presses a machine computer and a workstation which perform the control and regulation of the pressing operation.
It is also known to directly test, during the production, the pressing force to which a pellet is subjected. As is known, the pressing force is a measure for the tablet weight and tablet hardness. If the pressing force does not have the required value, for example, either the quantity of powder supplied per die and/or the setting of the pressure rollers is changed.
Finally, it is also known, for example, to measure the active substance in the pellets using a near infrared spectroscopy (NIR), or a laser fluorescence spectroscopy (LIF). Such a measurement can take place within the housing of the tablet press, either after the dies are filled, or during the ejection of the pellets from the dies.
It is the objective of the invention to specify a method for quality surveillance of pressed material in a rotary press, using which a rapid response to production changes is possible, and the loss ratio of pellets with insufficient quality features can be minimized.